OK, since nobody actually replied.....
Of course the idea has been discussed many times.
Visualization plug-in architecture was semi-promissed (like in 'we will really look into it'), and perhaps is not really *that* far away. Toby's (the guy who writes visuals, Prolux on this board) work is already in separate module. (Linux has a standard mechanism equivalent to dll's, but I think Toby uses something homebrewed.) I think it is now more or less the matter of finding enough time to design a nice, logical interface (including access to pre-processed audio like FFT spectra), document it, reorganize everything already written to fit into that scheme.... Ah, yes, another thing: limited processing power and semi-weird architecture more or less guarantee unsatisfactory results unless you write in Arm Assembly.
Menu system was originally supposed to had been written in Python and user-modifiable. However, there were issues with real-time scheduling in multithreaded environment and with performance. Search for Rob's clarifications (I always get this part wrong
)
DSP is, I think, a lost cause. Arm does not have enough power to handle software-only signal processing, and closing NDA with Phillips (in order to obtain reference documentation for their chip) involves slaughter of goats at midnight, selling your firstborn and some business with pentagrams and black candles.
Faced with closed player program and empeg guys too bussy to indulge more ephemeral of our whims, we were lucky enough to meet on this board Mark Lord, a Linux kernel hacker who writes three kernel modules before breakfast and another ten by lunch (after which he is off mountain-climbing). Scan Programming forum for a taste of his work.
Frankly, I don't know for what I would use comprehensive plug-in interface. In audio domain I don't think much more can be squized from DSP than the current excellent EQ. Dynamic compression was an issue, but Richard Lovejoy solved that by a nice kernel hack (and Mark made it easy to operate by one of his hacks). What is left is perhaps left-right delay and cross-fade (which is being discussed here and there). Toby's visuals are excellent, and I got my favourite one in the latest beta (TimeShade 128 - a voiceprint). I like user interface, and Mark made it much more tweakable than I can use. We have a handfull of different ways to back the player up, stream tunes from it, remotely control it... What's left?
Finally, one has to understand that we are talking specialized piece of hardware with slowish processor, strange display and 12MB of RAM total. Imagine what you can run in 12MB on Windows - not even Bob
Cheers!